Pigeonite is a common rock forming mineral that belongs to the pyroxene mineral group.  Pyroxenes are silicate minerals with varying amounts of calcium, iron and magnesium, and the pigeonite member has low calcium with relatively equal parts iron and Magnesium.  Pyroxenes are very common mineral group found in igneous rocks, and they crystallizes relatively quickly out of a cooling magma.

This dark and opaque mineral is not a particularly exciting to look at in hand sample, nor is it very useful. But pigeonite is interesting to Calvin at the moment as it is the primary mineral in the Apollo 15 lunar sample we currently have on display in the Dice Museum. Pigeonite crystals in our lunar sample are elongate, up to two centimeters in length, and is strongly chemical zoned, which is more obviously seen in the thin sections studied by NASA. Other minerals in the moon rock include the feldspar mineral anorthite, and the iron-titanium oxide ilmenite. Mineralogy is foundational not only to the geology of earth, but to any rocky mass in the universe. Our moon rock was collected from the lunar maria (the dark spots on the moon), and is the igneous rock basalt, which is formed when lava at the surface cools quickly.  Basalt is a rock that can be readily found on Earth.  This rock is exceptionally old, dated to 3.3 billion years old (for comparison, Earth is about 4.5 billion years old), so studying the moon gives us clues as to what the environment and geology of our early planet was like.

Come see our lunar sample in the Dice Museum now until February 15. The museum will be open this January right after the January Series each day, or by appointment!